Substrate for electroless plating, electroless plating structure, and electroless plating method

Abstract

The present invention relates to a substrate, for electroless plating, comprising a primer layer compatible with an electroless plating process. This substrate for electroless plating is constituted of a base material and a primer layer formed on one or both surfaces of the base material. The primer layer includes a thermoplastic resin I that constitutes a main agent component, and a resin II that constitutes a crosslinking agent component, and further includes a thermosetting resin III that has a bisphenol skeleton and constitutes an adhesive agent component. The resin III is preferably a bisphenol A type epoxy resin or a bisphenol F type epoxy resin. The content of the resin III in the primer layer is set to be 10% by mass to 48% by mass with respect to all of the resins constituting the primer layer. The substrate for electroless plating in the present invention exhibits good adhesion of a plating film via the primer layer.

Description

Electroless plating substrate, electroless plating structure, and electroless plating method

[0001] The present invention relates to a substrate for forming a plating film by electroless plating. More specifically, the present invention relates to a substrate for electroless plating that has a primer layer of a predetermined composition, and that has improved adhesion to the plating film compared to conventional techniques, and that can form a plating film with suitable quality and weather resistance.

[0002] Electroless plating has the advantage of being able to form plating films not only on conductive materials such as metals, but also on insulating materials such as metals, plastics, ceramics, organic compounds, cellulose, fabrics, and composites of these, and has been widely used industrially.

[0003] However, for plating substrates based on the above-mentioned insulating materials, film formation can be difficult depending on the type of plating film, etc. Therefore, when forming a plating film on a substrate made of an insulating material by electroless plating, it is common to form catalytic nuclei on the substrate surface and use these as starting points to promote deposition of the plating metal. There are several types of catalytic nuclei, and examples of these include applying a solution of metal salts (metal ions) or a dispersion of precious metal colloid particles to the substrate in advance.

[0004] The applicant of the present application has proposed an efficient process for forming a plating film in electroless plating, in which a predetermined resin layer called a primer layer is formed on the surface of the substrate before film formation, and a pretreatment solution containing nano-order precious metal colloid particles as catalyst nuclei is used (Patent Documents 1 to 3).

[0005] In the electroless plating process disclosed in Patent Document 1 by the applicant, a resin with a glass transition temperature (Tg) of 40°C or higher and 430°C or lower is used as a primer layer. After adsorbing and fixing precious metal nanoparticles onto the primer layer, the primer layer is fluidized by heat treatment within a range of ±50°C of the resin's glass transition temperature, causing the precious metal nanoparticles to sink into the primer layer. In this way, by applying a primer layer with predetermined properties and controlling the state of the precious metal nanoparticles, adhesion between the plating film on the primer layer and the substrate is ensured.

[0006] Furthermore, the electroless plating process developed by the present applicant can also be applied to the formation of fine circuits by compounding specific resins with the resins constituting the primer layer described above (Patent Documents 2 and 3). Specifically, a primer layer can be made of a two-component resin, in which a thermoplastic resin such as polyester is used as the main component (base resin) and a crosslinking agent such as an amine-based resin, a guanamine-based resin, or a melamine-based resin is mixed with this. This primer layer crosslinks and generates functional groups (amino groups) upon heat treatment or irradiation with light of 300 nm or longer. The functional groups act as acceptors that capture precious metal nanoparticles. These activated functional groups are then inactivated by irradiation with light of 300 nm or shorter (deep ultraviolet light irradiation). Such activatable and inactivatable functional groups can impart selective film-forming properties to the primer layer surface, allowing selective and fine plating films to be formed by applying a photomask or the like.

[0007] Patent No. 6312766 JP 2019-123909 A JP 2019-123910 A

[0008] In recent years, in fields such as electronic materials manufacturing and high-frequency circuit board material manufacturing, efforts to reduce transmission loss and insertion loss and increase the integration density of wiring have led to higher demands for plating films with higher levels of fineness, smoothness, adhesion to the substrate, and insulation performance between wiring (wiring patterns). The adhesion strength of plating films has also attracted attention in the semiconductor substrate manufacturing field, in addition to the aforementioned fields. For example, in the manufacture of interposers for semiconductor substrate manufacturing components, plating films with equivalent performance to those made of insulating materials are required. While silicon, resin, and other materials have traditionally been used as interposer materials, glass has recently attracted attention due to its cost and processability. However, no established manufacturing method for glass interposers, which are insulating materials, remains, and challenges remain, particularly in improving and maintaining the adhesion strength of wiring.

[0009] The adhesion strength of plating films formed by electroless plating was also an issue in the electroless plating process of Patent Document 1. However, the prior art's solution to the problem was insufficient, leaving room for improvement. That is, Patent Document 1 also evaluates the adhesion of plating films formed by this electroless plating process, so it can be said that it intended to ensure adhesion. Furthermore, this prior document also performs an adhesion test using a cross-cut method on the plating film after film formation, and a certain level of evaluation is achieved. However, this evaluation only determines whether or not the cross-cut plating film peels off, and does not indicate specific adhesion strength. Furthermore, according to the inventors' investigations, the content and results of such conventional evaluations are not sufficient to achieve the adhesion strength of plating films required in the various fields mentioned above.

[0010] Furthermore, while conventional adhesion evaluation of plating films has mainly focused on the initial adhesion immediately after electroless plating, evaluation of adhesion over time under constant temperature and humidity conditions is required for electronic materials, etc., as they are expected to be used under such conditions.

[0011] The present invention has been made in light of the above background, and provides a substrate for electroless plating having a primer layer applicable to the above-mentioned electroless plating process by the applicant of the present application, which can further improve the adhesion of the plating film. Specifically, the present invention clarifies a substrate that has an adhesion strength sufficient to withstand use in the various fields mentioned above and can exhibit adhesion even in a constant temperature and humidity environment.

[0012] The inventors conducted extensive research and concluded that optimizing the resin composition of the primer layer on the substrate was necessary to solve the above-mentioned problems. Possible methods for improving adhesion between the substrate (primer layer) and the plating film include roughening the surface of the primer layer to create irregularities and create an anchoring effect, or interposing an intermediate layer between the primer layer and the plating film to improve adhesion. However, roughening the surface of the primer layer may affect the surface morphology of the plating film formed thereafter. This is particularly true given the recent trend toward thinner plating films. Furthermore, the electroless plating process underlying this invention involves forming functional groups (acceptors) on the surface of the primer layer, to which precious metal nanoparticles, serving as catalytic nuclei, are bonded. Therefore, forming an intermediate layer on the surface of the primer layer would impede this film formation mechanism. Based on these findings, the inventors concluded that optimizing the composition of the primer layer itself is the best solution.

[0013] However, the adjustment of the primer layer configuration is premised on not interfering with the functions and properties of the primer layer in the electroless plating process that is the basis of the present invention. In this regard, the properties required as functions of the primer layer, taking into consideration the relationship between the primer layer and the substrate and the plating film that come into contact with the primer layer, include the following: (i) Adhesion at the interface between the substrate and the primer layer (ii) Strength of the primer layer itself (iii) Adsorption of precious metal nanoparticles (catalytic nuclei) on the surface of the primer layer (iv) Adhesion at the interface between the primer layer and the plating film

[0014] The present inventors have further investigated the composition of the primer layer and found that the adhesion strength of the plating film can be improved by ensuring the above-mentioned properties (i) and (iv), and that improving the rigidity of the primer layer is effective for this purpose. Specifically, they found that adding a thermosetting resin that can impart suitable adhesion to the primer layer is suitable.

[0015] However, even if the addition of a thermosetting resin to improve rigidity is effective in improving adhesion strength, it is necessary to consider the appropriate range of the amount added. The inventors' investigations into this point have confirmed that adding an excessive amount of thermosetting resin improves rigidity but reduces adhesion. This indicates that the primer layer requires both rigidity (hardness) and toughness (flexibility), and that the amount added should be determined taking into account the balance between the two. This leads to ensuring the properties (i) and (iv) above as well as the strength of the primer layer itself (ii).

[0016] Furthermore, when changing the composition of the primer layer by adding a thermosetting resin, it is also important not to impair the above characteristic (iii). The adsorption of precious metal nanoparticles on the surface of the primer layer is caused by functional groups (acceptors) generated from the crosslinking agent in the primer layer. The type and amount of the thermosetting resin used as the adhesive agent, as well as the balance with the content of other resins, can affect whether or not an effective acceptor can be formed on the surface of the primer layer.

[0017] Based on the above points, the present inventors have investigated suitable thermosetting resins and the amounts of thermosetting resins to be added, and have discovered that a plating film having excellent adhesion, plating properties, and surface morphology can be formed on a substrate having a primer layer containing a thermosetting resin of a predetermined structure in an appropriate range, thereby arriving at the present invention.

[0018] That is, the present invention provides a substrate for electroless plating comprising a base material and a primer layer formed on one or both sides of the base material, the primer layer containing a thermoplastic resin I as a main component and a crosslinking agent resin II, wherein the primer layer further contains a thermosetting resin III having a bisphenol skeleton as an adhesive component, and the content of resin III in the primer layer is 10% by mass or more and 48% by mass or less relative to all resins constituting the primer layer.

[0019] The structure and manufacturing method of the electroless plating substrate according to the present invention will be described below. Also, an electroless plating method using the electroless plating substrate according to the present invention and an electroless plated structure manufactured thereby will be described.

[0020] A. Constitution of the Electroless Plating Substrate According to the Present Invention As described above, the present invention essentially comprises a substrate and a primer layer formed on the substrate.

[0021] A-1 Substrate The substrate for electroless plating can be made of either a conductive material such as metal or an insulating material such as resin. By utilizing the properties of electroless plating, resin, plastic, glass, ceramic, cellulose, fabric, and composites of these can be suitably used as insulating materials.

[0022] In particular, in the field of electronic materials, etc., applications of resin substrates are increasing. Both thermoplastic resins and thermosetting resins can be used as insulating resin substrates. Examples of thermoplastic resins include polypropylene, polyethylene, polystyrene, acrylic, polyethylene terephthalate, polyphenylene ether, nylon, polyamide, polycarbonate, polyacetal, polyester, polybutylene terephthalate, polyphenylene sulfide, polyether ether ketone, polyurethane, polyimide, polyamide-imide, cyclic polyolefin, polyvinyl chloride, polyvinyl acetate, liquid crystal polymer, fluororesin, ABS resin, AS resin, etc. Examples of thermosetting resins include epoxy resin, phenolic resin, melamine resin, unsaturated polyester, urea resin, alkyd resin, polyurethane, thermosetting polyimide, etc.

[0023] As mentioned above, glass materials have been attracting attention in recent years as materials for semiconductor substrate interposers. The present invention makes it possible to form plating films with good adhesion even on glass substrates.

[0024] There are no particular limitations on the shape and dimensions of the substrate, which may be transparent, translucent, or opaque.

[0025] A-2 Primer Layer The primer layer in the present invention is a composite layer that essentially contains the three resins, Resin I, Resin II, and Resin III, described above, and is a mixture of these resins.

[0026] A-2-1 Resin I (Main Component) Resin I is a main component that serves as the framework for establishing the primer layer as a structure. Resin I, the main component, is a thermoplastic resin, and examples thereof include polyester resin, polyimide resin, LCP resin, and polyethylene terephthalate resin.

[0027] A-2-2 Resin II (Crosslinking Agent Component) Resin II, the crosslinking agent component, is a component that crosslinks intramolecular and intermolecular bonds of the resin that constitutes the primer layer through a crosslinking reaction, thereby insolubilizing the resin. In the electroless plating process of the present invention, it also functions as a component that generates functional groups (amino groups) during the crosslinking reaction. The generated functional groups act as acceptors that capture precious metal nanoparticles, as described below, and promote the formation of a plated thin film.

[0028] The crosslinking agent is not particularly limited as long as it has the above-described crosslinking reaction and functional group generation effects. Examples of suitable crosslinking agents include melamine-based crosslinking agents, amine-based crosslinking agents, guanamine-based crosslinking agents, and glycoluril-based crosslinking agents. Melamine-based crosslinking agents are particularly suitable. Examples of melamine-based crosslinking agents include methoxyalkyl melamines such as hexamethoxymethylmelamine, hexamethoxyethylmelamine (HMM), dimethoxymethylmelamine, trimethoxymethylmelamine, tetramethoxymethylmelamine, pentamethoxymethylmelamine, and hexamethoxymethylmelamine. Other examples include alkoxymethylglycolurils such as tetramethoxymethylglycoluril, 1,3-bismethoxymethyl-4,5-bismethoxyethyleneurea, and bismethoxymethylurea.

[0029] A-2-3 Resin III (Adhesion Agent Component) The above-mentioned Resin I and Resin II have been used as components of the primer layer in the electroless plating process (Patent Document 1) by the applicant of the present application. The resin constituting the primer layer in the present invention is a three-component resin that further contains Resin III, which serves as the adhesion agent component. The adhesion agent component does not itself function as a so-called adhesion agent. The adhesion agent component in the present invention is a component that improves the adhesion strength between the substrate and the plating film by imparting appropriate rigidity and toughness to the primer layer composed of Resin I and Resin II.

[0030] Resin III, an adhesive component, is a resin that imparts rigidity to the primer layer. Resin III is a thermosetting resin having a bisphenol skeleton. The bisphenol skeleton is a skeleton composed of two phenol groups, as shown in the following formula (1), and is known to include bisphenol A, bisphenol B, bisphenol C, bisphenol E, bisphenol F, bisphenol M, bisphenol P, bisphenol S, bisphenol Z, and phenoxy resins depending on the substituent R. The bisphenol skeleton is a structure that is effective in imparting rigidity and toughness to the resin.

[0031]

[0032] Resins III in the present invention are preferably resins having a bisphenol skeleton, and particularly preferably resins having a bisphenol A skeleton or a bisphenol F skeleton. Specifically, resins III are preferably bisphenol A-type epoxy resins or bisphenol F-type epoxy resins having epoxy groups. While biphenyl-type epoxy resins, glycidyl ester-type epoxy resins, and alicyclic epoxy resins are known as thermosetting resins having epoxy groups, these resins without a bisphenol skeleton are ineffective. Resins having an epoxy equivalent of 150 to 3,000 are preferred, and those having an epoxy equivalent of 170 to 500 are particularly preferred.

[0033] In the present invention, suitable adhesion to the plating substrate is imparted by controlling the content of Resin III in the primer layer. As described above, the addition of a thermosetting resin is effective in increasing the rigidity of the primer layer, but if the content is too high and the rigidity is too high, adhesion decreases. By appropriately adjusting the content of the thermosetting resin, the toughness of the primer layer can be ensured and optimal adhesion can be achieved. The content of Resin III is 10% by mass or more and 48% by mass or less, based on all resins constituting the primer layer. Preferably, it is 15% by mass or more and 40% by mass or less, and particularly preferably, it is 18% by mass or more and 38% by mass or less.

[0034] The content of each of Resin I and Resin II in the primer layer is not particularly limited as long as it is within the range of the content of Resin III. It is sufficient to set it within a range in which each resin can exert its function. Preferably, Resin I is 30% by mass or more and 80% by mass or less, more preferably 45% by mass or more and 75% by mass or less. Furthermore, Resin II is preferably 2% by mass or more and 25% by mass or less, more preferably 3% by mass or more and 20% by mass or less.

[0035] Furthermore, in the primer layer of the present invention, which is composed of a three-component system of resins I, II, and III, the ratio of the content of resin I to the content of resin III (resin I / resin III) is preferably 1 or more and 7 or less, and particularly preferably 1 or more and 4 or less. Resin I, the main component, is the resin that forms the backbone of the primer layer. The primer layer inherently exhibits adhesion as an intermediate layer between the plating film and the substrate, and also functions to capture and fix precious metal nanoparticles, which serve as catalyst nuclei. If the content of resin I is low relative to resin III, this basic function of the primer layer may be reduced, resulting in a decrease in the adhesion strength of the plating film. Therefore, the ratio of the content of resin I to the content of resin III is preferably 1 or more. On the other hand, in order for resin III, the adhesion agent component, to fully exert its function, it may be undesirable for the content of resin I, the main component, to be too high relative to resin III. Therefore, the ratio is preferably 7 or less, and particularly preferably 4 or less.

[0036] The contents of resins I, II, and III in the primer layer described above can be measured by Fourier transform infrared spectroscopy (FT-IR), near infrared spectroscopy (NIR), gas chromatography mass spectrometry (GC-MS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), nuclear magnetic resonance spectroscopy (NMR), or the like.

[0037] A-2-4 Other Components of the Primer Layer The primer layer of the electroless plating substrate of the present invention essentially comprises the above-described resins I, II, and III, but may also contain other components (resins and compounds). The primer liquid that serves as the precursor of the primer layer, described below, may contain a photoacid generator (PAG) or a sensitizer as a reaction initiator, and compounds derived from these are contained in the primer layer. The photoacid generator may also function as a curing accelerator for the above-described resin III. Examples of photoacid generators include onium salts (sulfonium salts, iodonium salts, diazonium salts, etc.), nitrobenzyl esters, diazomethane, triazines, and the like, used alone or in combination. Examples of sensitizers include 9-methylanthracene, anthracenemethanol, acenaphthylene, thioxanthone, methyl-2-naphthyl ketone, 4-acetylbiphenyl, and 1,2-benzofluorene. In the primer layer, the content of these compounds as reaction initiators is preferably 0.4% by mass or more and 10% by mass or less based on the total mass of the resins constituting the primer layer.

[0038] A-2-5 Primer Layer A preferred thickness for the primer layer formed on the substrate in the present invention is 0.05 μm or more and 1.5 μm or less. A thickness of less than 0.05 μm makes it difficult to form a plating film with sufficient adhesion in the subsequent electroless plating process. On the other hand, a primer layer exceeding 1.5 μm is undesirable because it may result in poor hardness and a loss of thin film and smoothness. The primer layer is more preferably 1.0 μm or less. The thickness of the primer layer can be adjusted by the concentration of the resin in the primer liquid and the application conditions, which will be described later. The glass transition temperature (Tg) of the primer layer having the above configuration is preferably 50°C or more and 350°C or less.

[0039] B. Method for Producing a Substrate for Electroless Plating According to the Present Invention The substrate for electroless plating according to the present invention can be produced by applying a primer solution containing Resin I, Resin II, and Resin III, which constitute the primer layer, and an appropriate reaction initiator, to a substrate, and then baking (prebaking) the applied primer solution at a predetermined temperature. In this case, the substrate described above is used.

[0040] The primer liquid, which is a precursor of the primer layer, is a solution in which Resin I, Resin II, Resin III and an appropriate reaction initiator are mixed and dissolved in a solvent.

[0041] Suitable solvents for the primer liquid include ketones, ethers, esters, and aromatic hydrocarbons. Specific examples of solvents include methyl ethyl ketone, methyl isobutyl ketone, 2-heptanone, cyclopentanone, cyclohexanone, 2-methoxy-1-propylene acetate, 2-methoxyethanol, 2-ethoxyethanol, 2-ethoxyethyl acetate, 1-methoxy-2-propyl acetate, 1,2-dimethoxyethaneethyl acetate, cellosolve acetate, propylene glycol monoethyl ether acetate, propylene glycol methyl ether acetate, methyl lactate, ethyl lactate, methyl pyruvate, ethyl pyruvate, ethyl 3-methoxypropionate, N-methyl-2-pyrrolidone, 1,4-dioxane, ethylene glycol monoisopropyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, and toluene.

[0042] As a result of dilution with the solvent, the concentration of each resin in the primer liquid differs from the content of each resin in the primer layer after baking. However, the blending ratio of each resin is the same for both the primer liquid and the primer layer. Regarding the composition of the primer liquid, the concentration of each resin relative to the total resin in the liquid is preferably 0.06% by mass or more and 17% by mass or less for Resin I, more preferably 2.0% by mass or more and 10% by mass or less for Resin II. Resin III is preferably 0.2% by mass or more and 12% by mass or less, more preferably 0.7% by mass or more and 6% by mass or less for Resin III. Furthermore, the concentration of the reaction initiator is preferably 0.007% by mass or more and 2% by mass or less, more preferably 0.02% by mass or more and 0.1% by mass or less for Resin III. The concentration of the solvent is preferably 80% by mass or more and 90% by mass or less for Resin II.

[0043] The primer liquid may have the above-described composition, and no other components are required. In particular, Resin III, the adhesive component, is a thermosetting resin, and its application typically requires the addition of a curing accelerator. The addition of such a curing accelerator is unnecessary when forming the primer layer of the present invention. This is because Resin III cures through a reaction with a photoacid generator or the like and the baking process described below. Furthermore, the addition of a curing agent may impair the function of the primer layer. For example, acid anhydrides such as tetrahydrophthalic anhydride, known as curing agents for bisphenol-type epoxy resins, may excessively increase the rigidity of the primer layer and reduce adhesion. Furthermore, low-molecular-weight amine compounds such as dicyandiamide may affect the generation of acceptors (functional groups) in the primer layer. Therefore, the addition of these curing accelerators to the primer liquid is not recommended.

[0044] The primer liquid can be prepared by sequentially adding and mixing each resin to a solvent. There is no restriction on the order in which the resins are added. Alternatively, stock solutions of each resin dissolved in a solvent may be mixed. Furthermore, a highly concentrated primer liquid may be prepared in advance and then diluted with a solvent.

[0045] The primer liquid can be applied to the substrate by various methods such as spraying, dipping, spin coating, roll coating, and various printing methods (screen printing, gravure printing, flexographic printing, inkjet printing, etc.).

[0046] The primer liquid applied to the substrate is then baked to form a primer layer, resulting in the electroless plating substrate of the present invention. The baking temperature is 150°C or higher and 260°C or lower. At temperatures below 150°C, it is difficult to form a good primer layer with sufficient adhesion. Furthermore, at temperatures above 260°C, it becomes difficult for the catalyst for plating deposition to adsorb. The baking temperature is preferably 180°C or higher and 240°C or lower. The baking process can be carried out in the air, or under reduced pressure or in a non-oxidizing atmosphere. During the baking process described above, the solvent in the primer liquid volatilizes and the resins harden. Furthermore, the crosslinking agent generates active functional groups (amino groups) on the surface of the primer layer, forming acceptors for the catalyst nuclei.

[0047] C. Electroless Plating Method According to the Present Invention In the electroless plating method according to the present invention, catalytic nuclei composed of noble metal nanoparticles are adsorbed onto the above-described electroless plating substrate, and then a plating film is formed by electroless plating. This electroless plating method may use a pre-prepared electroless plating substrate, or may be performed continuously from the preparation of the electroless plating substrate to the electroless plating step. In the latter case, the preparation of the electroless plating substrate is the same as that described above, and therefore, to avoid redundant description, the following will describe the steps after the preparation of the electroless plating substrate.

[0048] C-1 Pretreatment of Electroless Plating Substrate (Optional Step) As described above, the primer layer of the electroless plating substrate according to the present invention has functional groups (amino groups) on its surface that act as catalyst nuclei acceptors due to the action of Resin II as a crosslinker component. The functional groups generated by the application and baking of the primer solution are active and can adsorb precious metal nanoparticles in this state. The functional groups on the primer layer are then inactivated by irradiation with deep ultraviolet light having a wavelength of 300 nm or less. The inactivation of such functional groups by light irradiation contributes to the selective fixation of precious metal nanoparticles. That is, by performing patterning using a photomask or the like and selectively inactivating the functional groups by irradiation with deep ultraviolet light, it is possible to form a pattern of active functional groups on the substrate. Therefore, by performing the patterning and light irradiation before adsorption of precious metal nanoparticles, a desired wiring pattern can be formed using an electroless plating film. This step of forming a pattern of functional groups by irradiation with deep ultraviolet light is optional.

[0049] When irradiating the primer layer with deep ultraviolet light having a wavelength of 300 nm or less to inactivate the functional groups on the primer layer, the process can be the same as that commonly used in the semiconductor field. As a light source, ultraviolet lamps such as low-pressure mercury lamps and excimer lamps can be used. Low-pressure mercury lamps can irradiate ultraviolet light with wavelengths of 185 nm and 254 nm. As an excimer lamp, Xe ２ Examples of light sources that can be used include an excimer lamp (wavelength 172 nm), a KrBr excimer lamp (wavelength 206 nm), a KrCl excimer lamp (wavelength 222 nm), and a KrF excimer lamp (wavelength 248 nm). Using these light sources and an appropriate photomask, a desired functional group pattern can be formed. Patterning is also possible using ultraviolet laser light or the like.

[0050] C-2 Noble Metal Nanoparticle Adsorption Process Noble metal nanoparticles that serve as catalytic nuclei for plating film deposition are adsorbed onto the primer layer surface of a substrate that has been appropriately patterned, etc. The noble metal nanoparticles are fine particles made of a noble metal, with an average particle size of 1 nm to 100 nm. Preferable noble metals are Au, Pt, and Pd, which have suitable catalytic properties. The noble metal nanoparticles are preferably in a monodispersed state, and since particles with a particle size that is too small tend to aggregate, the particle size should be 1 nm or greater. Furthermore, noble metal nanoparticles with an excessively large particle size have a reduced ability to bond with functional groups in the primer layer. The average particle size of the noble metal nanoparticles is more preferably 3 nm to 30 nm.

[0051] A preferred method for adsorbing and fixing precious metal nanoparticles to the primer layer is to apply a dispersion of precious metal nanoparticles to the surface of the primer layer. In this case, an aqueous solution containing a sugar alcohol is preferred as the dispersion medium for the dispersion of precious metal nanoparticles. The sugar alcohol acts as a protective agent (dispersant) surrounding the precious metal nanoparticles and suppresses aggregation of the precious metal nanoparticles in the dispersion. Furthermore, the sugar alcohol bonded to the precious metal nanoparticles in the dispersion is substituted with functional groups on the surface of the primer layer, promoting bonding between the precious metal nanoparticles and the functional groups of the primer layer. Examples of sugar alcohols that can be used as such protective agents include glycerin, erythritol, xylitol, sorbitol, and mannitol. The dispersion medium is preferably an aqueous solution containing 0.1 g / L or more and 20 g / L or less of a sugar alcohol.

[0052] The dispersion of noble metal nanoparticles can be applied by spraying, dipping, using a spin coater, a roll coater, etc. After application of the dispersion, drying and washing may be carried out as necessary.

[0053] C-3 Electroless Plating Process A plating film is formed by electrolessly plating a substrate onto which noble metal nanoparticles have been adsorbed. The present invention can be applied to the electroless plating of various metals. Metals that can be used to form films by electroless plating include noble metals such as Au, Ag, Pt, and Pd, and base metals such as Cu, Ni, and Co. Known compositions of the electroless plating solution and electroless plating methods and conditions for the electroless plating of these metals can be applied.

[0054] For example, autocatalytic electroless plating solutions are widely known for gold, which is widely used as a wiring material for electronic materials, semiconductor substrates, and the like. Autocatalytic electroless plating solutions contain an gold salt (gold ions), a reducing agent for reducing the gold ions, and appropriate additives. Preferably, a non-cyanide electroless plating solution is used. Suitable gold salts for use in autocatalytic plating solutions include tetrachloroauric acid (III), chloroauric acid (III), gold (I) chloride, gold (III) trifluoride, gold (I) monofluoride, gold (I) monobromide, gold (III) tribromide, hydroxygold (III) oxide, gold (III) triiodide, gold (III) trisnitrate, gold (I) nitrate, gold (I) sulfite salt, and hydrates or salts thereof. Known reducing agents for electroless plating solutions include formaldehyde, hydrazine, ascorbic acid, thiourea, hydroquinone, dimethylamine borane, hypophosphite, hydrogen peroxide, formic acid, hypophosphite, boron hydride, thiosulfuric acid, hydroxylamine, and sodium erythorbate, with ascorbic acid, boron hydride, hydroquinone, and formaldehyde being preferred.

[0055] C-4 Post-heat treatment step (curing step) The electroless plating step described above forms a plating film on the primer layer, essentially completing the electroless plating method of the present invention. However, to ensure the adhesive strength between the plating film and the substrate, it is preferable to add a post-heat treatment step. This post-heat treatment step involves heating at a temperature above the glass transition temperature to fluidize the primer layer and embed the noble metal nanoparticles in the primer layer.

[0056] The heating temperature in the post-heat treatment step is preferably within ±50°C of the glass transition temperature (Tg) of the primer layer, and is preferably 200°C or higher and 300°C or lower. Within this range, the primer layer becomes fluidized, and the noble metal nanoparticles are incorporated into the primer layer, increasing the adhesion strength. This heat treatment can be performed in an air atmosphere, but can also be performed in a reduced pressure atmosphere or a non-oxidizing atmosphere. The heating time is preferably 0.1 hours or higher and 2 hours or lower.

[0057] The post-heat treatment step ensures adhesion between the plating film and the substrate (primer layer). After the post-heat treatment step, post-treatment such as plasma ashing may be performed as needed.

[0058] D Electroless Plated Structure According to the Present Invention An electroless plated structure can be obtained by the electroless plating substrate and electroless plating method according to the present invention described above. This electroless plated structure is composed of the above-mentioned substrate and primer layer, and at least one metal plating film formed on the primer layer. In this case, the plating film formed on the primer layer is a plating film formed by electroless plating. When a further plating film is formed on the electroless plating film, the plating film may be an electroless plating film or an electrolytic plating film. There are no particular limitations on the thickness of each plating film.

[0059] In addition, the electroless plated structure according to the present invention does not require the presence of noble metal nanoparticles applied to the substrate during the manufacturing process. When the same type of noble metal is used for the noble metal nanoparticles and the plating film (for example, when Au nanoparticles are used as catalytic nuclei and Au plating is performed on top of them), the noble metal nanoparticles are integrated with the plating film and do not form a separate structure. Furthermore, even if the noble metal nanoparticles and the plating film are made of different metals, if the noble metal nanoparticles are fine, they may diffuse into the metal of the plating film and not be recognized as a separate structure.

[0060] As explained above, the electroless plating substrate according to the present invention can improve the adhesion strength of the plating film to a level higher than conventional levels by optimizing the configuration of the primer layer. The adhesion strength of the plating film according to the present invention is good not only in the initial state but also in a constant temperature and humidity environment. Furthermore, the electroless plating method using the primer layer according to the present invention can form a plating film of a desired pattern in a relatively simple manner while ensuring adhesion.

[0061] First Embodiment: Hereinafter, an embodiment of the present invention will be described. In this embodiment, a substrate for electroless plating was manufactured by forming a primer layer on the primer layer used in the prior art (Patent Document 1) while adjusting the content of the thermosetting resin serving as an adhesive component. Then, electroless plating of a gold plating film was performed, and the change in the adhesion of the gold plating film depending on the content of the thermosetting resin serving as an adhesive component was examined.

[0062] The primer layer was formed by dissolving a polyester resin (UPICACOAT GV-110, manufactured by Japan U-Pica Corporation) as resin I (main component), a melamine resin (CYMEL (registered trademark) 303LF, manufactured by Allnex) as resin II (crosslinking agent component), a bisphenol A-type epoxy resin (jER828, manufactured by Mitsubishi Chemical Corporation) as resin III (adhesion agent component), and a photoacid generator (CYCAT (registered trademark) 4040, manufactured by Allnex) in a cyclohexane solvent, and then coating and baking the primer liquid on the substrate.

[0063] In this embodiment, ten types of primer layers (primer layer A to primer layer J) were formed using ten types of primer liquids (primer liquid A to primer liquid J) with different compositions based on Resin I, Resin I, and Resin III. In addition, to compare this embodiment with the prior art, a primer liquid (primer liquid K) that did not contain bisphenol A-type epoxy resin, which is Resin III (adhesive agent component), was prepared and a primer layer (primer layer K) was formed. The resin compositions of the primer liquids evaluated in this embodiment are as shown in Table 1.

[0064]

[0065] To form a primer layer after applying the primer liquid, 4 mL of the primer liquid was applied to a glass substrate (dimensions: 10 cm x 10 cm) by spin coating. The substrate after applying the primer liquid was then prebaked to remove the solvent and form primer layers (primer layer A to primer layer K). The prebaking was performed by heating in an air atmosphere in a forced circulation oven at 260°C for 30 minutes. The composition of each formed primer layer was measured by combined analysis using gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy.

[0066] Next, a gold plating film was formed on the electroless plating substrate manufactured by the above process. In this embodiment, the surface of the primer layer was exposed to light in a predetermined pattern to partially deactivate the acceptors (amino groups). The exposure process used a photomask to form a linear pattern (L / S = 5 μm) with a width of 5 μm and an interval of 5 μm. A deep ultraviolet light exposure machine (Deep UV Multilight, manufactured by Ushio Inc.) was used to irradiate the surface with deep ultraviolet light at a wavelength of 254 nm at 800 mJ / cm. ２ Irradiated with.

[0067] Then, an Au nanoparticle dispersion (SEADCAT (registered trademark) CAT Au-10, manufactured by EEJA Corporation) was applied to the surface of the substrate (primer layer) after the exposure treatment as precious metal nanoparticles that would become catalytic nuclei. This Au nanoparticle dispersion was a dispersion of Au nanoparticles with a particle size of 16 nm. In the Au nanoparticle dispersion application treatment, the substrate was immersed in the dispersion at room temperature for 15 minutes and then dried in the atmosphere.

[0068] After the Au nanoparticles were fixed to the primer layer, an Au plating film was formed by electroless plating. An Au electroless plating solution (AC FAB (registered trademark) AU-ACG3000GX, manufactured by EEJA Corporation) was used as the electroless plating solution, and the Au plating film was formed at a plating temperature of 65°C for a plating time of 5 minutes. These plating conditions were intended to result in an Au plating film with a thickness of 50 nm.

[0069] After the formation of the Au plating film, a heat treatment (curing process) was performed to sink the Au nanoparticles into the primer layer. The curing process involved heating in air at 260°C for 30 minutes in a static oven. Through these processes, an Au plating film was formed on the electroless plating substrates of each Example, Conventional Example, and Comparative Example.

[0070] Finally, a Cu plating film was formed on the Au plating film formed above. The Cu plating was performed using a commercially available electrolytic Cu plating solution (MICROFAB (registered trademark) Cu250, manufactured by EEJA Corporation) at a current density of 3 A / dm ２ The copper plated film was subjected to electrolytic plating treatment at 4000 kJ / min for 20 minutes to form a Cu plating film having a thickness of about 15 μm.

[0071] After the Cu plating film was formed, the adhesion (adhesion strength) of the plating film was evaluated. The evaluation of adhesion strength was based on the peel strength obtained by a peel test (test conditions: 90° tensile test according to JIS K 6854-1). The pass value in the cross-cut test evaluation in the prior art (Patent Document 1) is 0.2 to 0.3 N / mm when converted to the peel strength in the peel test employed in this embodiment. With reference to this, in this embodiment, samples with a peel strength of 0.4 N / mm or more were judged to pass. The evaluation results are shown in Table 2, along with the compositions of each primer layer (primer layer A to primer layer K).

[0072]

[0073] Looking at Table 2 for the effect of the thermosetting resin (resin having a bisphenol skeleton) which is the adhesive agent component (resin III), the substrates having primer layers A to G have improved adhesion strength compared to the substrate having the conventional primer layer K. This suggests that the addition of the thermosetting resin having a bisphenol skeleton which is the adhesive agent component works favorably in the configuration of the primer layer.

[0074] However, it is also undesirable to add an excessive amount of the bisphenol skeleton resin, which is an adhesive agent component. This is because the primer layers of the electrolessly plated substrates having primer layers H to J contain an excess of adhesive agent components exceeding 48% by mass, resulting in lower adhesion strength than primer layer K, which does not contain an adhesive agent component. Furthermore, the results of primer layer J, which has extremely low adhesion strength, show that the thermoplastic resin (polyester resin), which is the main component (resin I), is essential for the primer layer.

[0075] Second Embodiment: From the results of the study of the first embodiment, it was confirmed that adding a thermosetting resin having a bisphenol skeleton to the primer layer can improve the adhesion of the plating film. In this embodiment, these electroless plating substrates were evaluated for the adhesion strength of the plating film, as well as the patternability and environmental resistance (moisture resistance) of the plating film. Furthermore, the characteristics were also examined when the pre-baking conditions during primer layer formation were changed. In this embodiment, a detailed study was conducted on electroless plating substrates having primer layers A, B, E, F, and G of the first embodiment (these are referred to as Examples 1-1 and 1-2, Examples 2-1 and 2-2, and Examples 3 to 5). Furthermore, in this embodiment, a comparison was made with primer layer K, which does not contain a thermosetting resin having a bisphenol skeleton (these are referred to as Conventional Examples 1-1 and 1-2).

[0076] The primer liquids used to form the primer layer were primer liquids with the same composition as in the first embodiment (primer liquids A, B, E, F, G, and K). The primer layer formation process was also basically the same as in the first embodiment. However, in this embodiment, the primer layers were formed at a pre-bake temperature of 180°C (Examples 1-1 and 2-1, Conventional Example 1-1) and 240°C (Examples 1-2, 2-2, Examples 3 to 5, Conventional Example 1-2). In addition, in this embodiment, a photomask with an L / S (line and space) of 5 μm / 5 μm was used to form the primer layer, and deep ultraviolet light with a wavelength of 254 nm was applied at 1000 mJ / cm. ２ Irradiated with.

[0077] Then, the same Au nanoparticle dispersion as in the first embodiment was applied to fix the Au nanoparticles on the surface of the primer layer, and then an Au plating film was formed by electroless plating. The electroless plating solution and plating conditions were the same as in the first embodiment. After the formation of the Au plating film, a curing process was carried out under the same conditions as in the first embodiment.

[0078] In this embodiment, in addition to the adhesion strength (initial adhesion strength) of the Au plating film, the film thickness and surface roughness of the Au plating film were measured to confirm the quality of the plating performance affected by the substrate, and the clarity (fine wiring performance) of the plating film in the above-mentioned pattern (L / S: 5 / 5 μm) was also confirmed. The film thickness was measured using an X-ray fluorescence analyzer (EA6000VX, Kitahama Seisakusho Co., Ltd.). The surface roughness (Sa) was measured using a white light interference microscope (VS1330, Hitachi High-Tech Corporation). The fine wiring performance of the plating film was also visually evaluated based on the presence or absence of pinholes on the plating film surface, the presence or absence of metal deposition outside the set pattern, and whether the color of the plating film was standard.

[0079] Furthermore, in this embodiment, a humidity accelerated test was conducted to evaluate adhesion over time in a constant temperature and humidity environment. In this evaluation test, each plated substrate was exposed to an atmosphere maintained at a temperature of 85°C and a relative humidity of 85%, and the adhesion strength of the plated substrate was measured after 50 hours. Note that the adhesion strength (initial adhesion strength) and humidity accelerated test were evaluated after Cu plating (electroplating) treatment, as in the first embodiment.

[0080] In this embodiment, the measurement results of adhesion strength (initial adhesion strength), surface roughness (Sa), thickness of the Au plating film, and durability (humidity accelerated test) were evaluated as "excellent (◎)," "good (◯)," "poor (△)," and "unacceptable (×)" according to the criteria shown in Table 3 below. The results of the above evaluation tests conducted on the Au-plated substrate manufactured in the second embodiment are shown in Table 4.

[0081]

[0082]

[0083] As can be seen from Table 4, the basic tendency is that the quality (film thickness, surface roughness, clarity) of the Au plating film is good on the electroless plated substrates of Examples 1-1 and 1-2 (primer layer A), Examples 2-1 and 2-2 (primer layer B), Examples 3 to 5 (primer layers E, F, G), and Conventional Example 1-1 (primer layer K). In other words, it can be said that the electroless plating substrates having the conventional primer layer also have properties suitable for the formation of the Au plating film itself.

[0084] However, in an evaluation that took into account the adhesion strength of the plating film, the primer layers of Conventional Examples 1-1 and 1-2, which do not contain Resin III (a curable resin having a bisphenol skeleton), an adhesion agent component, showed insufficient results. This point is the same as the evaluation in the first embodiment. Furthermore, the conventional examples showed no ability to meet the adhesion strength requirements under a constant temperature and humidity environment. Furthermore, the primer layer K of the conventional example required a relatively low pre-baking temperature (180°C); pre-baking at a high temperature (240°C) failed to form an Au plating film (Conventional Example 1-2).

[0085] Furthermore, the electrolessly plated substrates of Examples 1-1 and 1-2 (primer layer A), Examples 2-1 and 2-2 (primer layer B), and Examples 3 to 5 (primer layers E, F, and G) exhibited effective adhesion strength even in a humidity accelerated test (temperature 85°C, relative humidity 85%, 50 hours). These results confirm that adding an appropriate amount of Resin III, which serves as an adhesion agent component, can impart unprecedentedly favorable adhesion strength to the primer layer.

[0086] Based on the above results, in order to confirm the long-term durability of adhesion, Examples 1-1 and 1-2 (primer layer A) and Examples 2-1 and 2-2 (primer layer B), which received an excellent (◎) rating in all evaluations, were subjected to a humidity accelerated test (temperature 85°C, relative humidity 85%) for 500 hours. As a result, the electroless plated substrates of these Examples showed an adhesion strength of 30% or more (rating: ○) even after 500 hours, confirming their good long-term durability.

[0087] Third Embodiment: In this embodiment, a bisphenol F-type epoxy resin (jER806H, manufactured by Mitsubishi Chemical Corporation) and a phenoxy resin (jERYX7200B35, manufactured by Mitsubishi Chemical Corporation) were used as the curable resin having a bisphenol skeleton, which was Resin III, an adhesive component. Furthermore, a guanamine-based resin (BX-4000, manufactured by Nippon Carbide Industries Co., Ltd.) and an amino-based resin (NK-350, manufactured by Nippon Shokubai Co., Ltd.) were used as Resin II, a crosslinking agent component. Primer layers were then formed using primer solutions (Primer Solutions L, M, and N) that combined Resins II and III with the same Resin I as in the first embodiment, to produce substrates for electroless plating (Primer Layers L (Example 6), M (Example 7), and N (Example 8)).

[0088] Furthermore, for comparison with the above Examples, a substrate for electroless plating having a primer layer made of a primer solution (primer solution O) containing an alicyclic epoxy resin (Celloxide 2021P, manufactured by Daicel Corporation) as resin III, which is a resin not having a phenol skeleton, was also produced (primer layer O: comparative example).

[0089] Then, Au plating and Cu plating were performed on these substrates for electroless plating, and the adhesion of the plating film was evaluated. The composition of the primer solution prepared in this embodiment is as follows.

[0090]

[0091] In the preparation of the electroless plating substrate, the above-mentioned various primer solutions were applied to the same glass substrate as in the first embodiment and prebaked to form a primer layer. The process was the same as in the first embodiment, and the prebaking temperature was 240° C. In the primer layer formed at this time, the content of each resin was the same as the ratio to all resins in the primer solution.

[0092] After the primer layer was formed, Au plating (electroless plating) and Cu plating (electrolytic plating) were performed in the same manner as in the first embodiment. Then, the characteristics of the plating film formed by the electrolessly plated substrates having each primer layer were evaluated using the same test methods and evaluation criteria as in the second embodiment. The results are shown in Table 6.

[0093]

[0094] The results of Examples 6 to 8 in Table 6 confirm that primer layers (primer layers L, M, and N) exhibiting favorable initial adhesion and durability can be formed by using a thermosetting resin having a bisphenol skeleton as the adhesion agent component (resin III). It was also confirmed that resins other than melamine-based resins can be used as the crosslinker component (resin II).

[0095] On the other hand, in the case of the electroless plating substrate having a primer layer in which the alicyclic resin without a bisphenol skeleton of the comparative example (primer layer O) was used as resin III, no Au plating film was formed. The reason for this is thought to be that acceptors (functional groups) were not properly formed on the primer layer surface, and thus noble metal nanoparticles serving as catalyst nuclei were not adsorbed. Therefore, even if a thermosetting resin is added to the primer layer as an adhesion agent component, care must be taken when selecting the resin.

[0096] Fourth Embodiment: In this embodiment, a resin substrate was used as the base material for the electroless plating substrate, and a primer layer was formed. The resin substrates used in this embodiment were LCP resin (Vextar, manufactured by Kuraray Co., Ltd.), PPS resin (Torelina, manufactured by Kuraray Co., Ltd.), and PEEK (EXPEEK, manufactured by Kurabo Industries Co., Ltd.). These substrates were in the form of films measuring 100 mm x 100 mm and 20 μm to 200 μm thick (Examples 9 to 11).

[0097] The primer layer B of the first embodiment was formed on each of the above-mentioned various substrates. The composition of the primer liquid (primer liquid B) was the same as in the first embodiment. The primer layer application method and other procedures were the same as in the first embodiment, and the pre-baking temperature was 240°C. Then, Au plating films and Cu plating films were formed in the same manner as in the first embodiment. Thereafter, the characteristics of the plating films formed on the electrolessly plated substrates of this embodiment were evaluated using the same test methods and evaluation criteria as in the second embodiment. The results are shown in Table 7.

[0098]

[0099] From Table 7, it was confirmed that the primer layer of the three-component system (resin I, resin II, resin III) applied in the present invention is also effective for resin substrates.

[0100] The electroless plating substrate according to the present invention has a primer layer composed of a three-component system (resin I, resin II, and resin III), with resin III containing a predetermined thermosetting resin for improving adhesion. By optimizing the primer layer configuration, the present invention ensures higher adhesion than conventional methods. The electroless plating substrate according to the present invention can be suitably used in electroless plating processes for forming various wiring and electrodes in fields such as electronic material manufacturing and high-frequency substrate material manufacturing. Furthermore, the present invention can form a plating film with good adhesion even when glass is used as the substrate. The present invention is also useful for manufacturing interposers in semiconductor substrate manufacturing components, where the use of glass substrates has been considered in recent years.

Claims

1. A substrate for electroless plating comprising a base material and a primer layer formed on one or both sides of the base material, the primer layer containing a thermoplastic resin I as a main component and a crosslinking agent resin II, wherein the primer layer further contains a thermosetting resin III having a bisphenol skeleton as an adhesive component, and the content of resin III in the primer layer is 10% by mass or more and 48% by mass or less of all the resins constituting the primer layer.

2. The substrate for electroless plating according to claim 1, wherein resin I is a polyester resin, a polyimide resin, an LCP resin, or a polyethylene terephthalate resin, and resin II is a resin containing an amino group.

3. The substrate for electroless plating according to claim 1 or 2, wherein the ratio of the content of resin I to the content of resin III is 1 or more and 7 or less.

4. A method for manufacturing a substrate for electroless plating according to claim 1 or 2, comprising the steps of: applying a primer liquid containing resin I as a main component, resin II as a crosslinking agent component, and resin III as an adhesive component onto a substrate; and baking the applied primer liquid at a temperature of 150°C or higher but 260°C or lower to form a primer layer.

5. An electroless plating method for forming a metal plating film on a substrate by electroless plating, comprising the steps of: applying a primer liquid onto the substrate, the primer liquid containing resin I as a main component, resin II as a crosslinker component, and resin III as an adhesive component; baking the applied primer liquid at 150°C or higher and 260°C or lower to form a primer layer; dispersing a noble metal nanoparticle catalyst made of a noble metal with a particle size of 1 nm or higher and 100 nm or lower on the surface of the primer layer; and forming a thin gold film on the surface of the primer layer using an electroless plating liquid.

6. An electroless plated structure comprising a substrate for electroless plating according to claim 1 or 2, and an electroless plated film made of metal formed on the surface of the primer layer of said substrate for electroless plating.

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